Method for preparing binary saline or ionic hydrides

ABSTRACT

A PROCESS COMPRISING REACTING HYDROGEN AND A METAL ME IN THE PRESENCE OF COMPOUNDS OF THE GENERAL FORMULA MERQR WHEREIN Q IS AN ALKOXYL, AROXYL OR ARALKOXYL SELECTED FROM THE GROUP CONSISTING OF SUBSTITUENTS DERIVED FROM ETHERALCOHOLS OBTAINABLE BY THE ALKLATION OF ONE HYDROXYL GROUP IN DIOLS AND IN POLYGLYCOLS, AND SUBSTITUENTS DERIVED FROM ETHERALCOHOLS OBTAINABLE BY ALKYLATION OF TWO HYDROXYL GROUPS IN TRIOLS AND SUBSTITUENTS DERIVED FROM AMINOALCOHOLS OF THE GENERAL FORMULA   R2-HNHHCNH2NOH   WHEREIN R IS AN ALKYL, H IS 0, TO 1, OR 2, AND N IS AN INTEGER BETWEEN 1 AND 15; AND ME IS AN ALKALI METAL, AN ALKALINE EARTH METAL, B, AL OR SI; AND R IS THE VALENCE OF ME.

United States Patent 3,591,339 METHOD FOR PREPARING BINARY SALINE ORIONIC HYDRIDES .laroslav Vit, Vladimir Prochazka, and Bohuslav Casensky,Prague, Jiri Machacek, Krumvir, and Josef Vlk, Prague, Czechoslovakia,assignors to Ceskoslovenska akademie ved, Prague, Czechoslovakia NoDrawing. Filed May 15, 1967, Ser. No. 638,576 Claims priority,application Czechoslovakia, May 17, 1966, 3,299/66 Int. Cl. Ctllb 6/04U.S. Cl. 23-204 14 Claims ABSTRACT OF THE DISCLOSURE A processcomprising reacting hydrogen and a metal Me in the presence of compoundsof the general formula Me Q wherein Q is an alkoxyl, aroxyl or aralkoxylselected from the group consisting of substituents derived frometheralcohols obtainable by the alkylation of one hydroxyl group indiols and in polyglycols, and substituents derived from etheralcoholsobtainable by alkylation of two hydroxyl groups in triols andsubstituents derived from aminoalcohols of the general formula wherein Ris an alkyl, h is 0, 1, or 2, and 12 is an integer between 1 and 15; andMe is an alkali metal, an alkaline earth metal, B, Al or Si; and r isthe valence of Me.

BRIEF SUMMARY OF THE INVENTION This invention relates to the preparationof binary saline or ionic hydrides i.e. hydrides of alkali metals andalkaline earth metals including magnesium in finely powdered form andparticularly hydrides of such elements as lithium, sodium, potassium,magnesium, calcium and the like. The properties of magnesium hydrideappear to be somewhere between the ionic hydrides and covalent hydride.Thus, magnesium hydride can be considered to be a transition hydridebetween ionic and covalent hydrides. For convenience, it will beconsidered along with the ionic hydrides in this application.

Hydrides of alkali metals and of alkaline earth metals are frequentlyused as initial substances for a number of inorganic processes. Theyform either the base material for the production of differentsubstances, particularly complex hydrides, or they are used in diiferentbranches of the chemical industry as valuable ingredients for instanceas descaling agents in metallurgy for the pickling of steel sheets orplates, in the building trades as a foaming agent for lightweight porousbuilding materials, in organic chemistry as alkylation and condensationagents or as siccatives and the like.

The preparation of these substances for industrial applicationsgenerally presents no difliculty since a product of superior purity andquality is ordinarily not required. The preparation of very pureproducts of superior quality with a large specific surface or surfacedistension has, however, not yet been achieved to a satisfactory degree.

For instance, if an interaction of pure lithium with electrolyticalhydrogen of high purity takes place, a sinterlike substance results,which frequently contains metallic lithium either in a dispersed form ordissolved in lithium hydride. The preparation of lithium hydride havinga large specific surface or surface distension i.e. in powdered form hasnot heretofore been achieved satisfactorily (see for instance AlbertMahe, Bull. Soc. Chem. France 1165/ 1950).

A certain increase of the specific surface or surface distension can beachieved by using as an initial substance 3,591,339 Patented July 6,1971 a mixture of lithium oxide or lithium chloride and metallicmagnesium (see US. Pats. 2,468,260 and 2,606,100). The thus preparedlithium hydride is equally sinter-like but can be more easily ground.The large specific surface or surface distension which is, however,frequently required cannot be achieved by this technique.

Similar conditions prevail in preparing potassium or sodium hydride, seeT. R. P. Gibb, Progress in Inorganic Chemistry 3 (1962), 315. The alkalimetals and alkaline earth metals suffer a volume contraction during theprogress of adsorption of hydrogen gas into the metal surface becausethe density of the resulting hydrides is larger than that of the freemetal, resulting in a barrier to further adsorption of hydrogen gas, andthus to the production of further hydride. Similar difficulties alsooccur during the hydriding of calcium with the difference that theinteraction proceeds in part between the solid metal and hydrogen gasand only after a mixture with a lower melting point than calcium hasbeen formed also between the melt and the gas. As an undesirablesinter-like form of calcium hydride results, a mixture of anhydrouscalcium chloride CaCl with metallic sodium instead of free calcium mustbe hydrided, similar to the case with lithium. The powdered product isobtained from the sinterlike mass either by grinding (see US. Pat.2,702,234) or by eliminating the sodium chloride from the sinter-likemass by washing the same with liquefied ammonia (see US. Pat.2,702,740). This technique is not particularly effective and moreover isvery laborious and does not produce a hydride of sufficiently largespecific surface or surface distension.

Saline or ionic hydrides of alkali metals and alkaline earth metalshaving a suflicient surface distension cannot 'be obtained, with thesingle exception of sodium hydride in oil suspension, by directhydriding of these metals or their compounds. As these interactions donot proceed in a quantitative manner and, with the above said singleexception, produce hydrides contaminated with non-consumed metals (whichmay be either dissolved or enclosed in the sinter-like mass), suchhydrides cannot be used for technical purposes in many cases. Theseconditions exist as the saline or ionic hydrides are used both inorganic or inorganic chemistry predominantly for reactions, proceedingin organic solvents, in which all saline or ionic hydrides areinsoluble. Therefore their specific surface or surface distension mustbe as large as possible in order that the interaction can proceed in areasonable time even in a medium in which they are insoluble.

Even by grinding the sinter-like hydride, there cannot be obtained aslarge a specific surface or surface distension as is possible, withoutgrinding, by direct interaction in a reactor yielding the resultinghydride in powder form. In addition, the grinding of hydrides requiresgreat care and is a difficult operation not only due to theirextraordinary sensibility to moisture and to oxygen (whereby in somecases the grinding cannot be performed even in a nitrogen atmosphere),but also because the dispersed softened metal sticks to the grindingmeans. The free metal remaining as an impurity can cause undesiredadditional chemical reactions and makes the handling of the hydridesdifiicult.

Other methods for preparation of saline or ionic hydrides of alkalimetals or alkaline earth metals with a large specific surface or surfacedistension produced by direct interaction have been therefore keenlysought.

In connection therewith, a number of catalysts and techniques have beenproposed which, for some hydrides, are partially satisfactory but onlyin a single case i.e. in the preparation of sodium hydride, has asatisfactory product with a large specific surface or surface distensionbeen obtained. This has been achieved by hydriding sodium sus- 3 pensionin an inert organic liquid, advantageously in paraffin oil (see US.Pats. 1,958,012 and 2,021,567).

This technique, however, can only be applied for the preparation of puresodium hydride by the hydriding of pure sodium. The preparation of amixture of sodium hydride with another alkali metal or alkaline earthmetal hydride by hydriding a sodium alloy, results in a product having asurface distension smaller by several orders. It is impossible toprepare in this way the remaining binary saline or ionic hydrides ofalkali metals or alkaline earth metals with sufliciently large surfacedistension.

No additional promotor is known at present which would enable thepreparation of all hydrides of alkali metals and alkaline earth metalswith a large surface distension by hydriding these metals and whichwould enable a direct preparation of mixtures of these metal hydrides,having large surface distension by direct interaction of alloys of thesemetals with hydrogen gas.

It is an object of this invention to provide a process for preparingpowdered saline or ionic hydrides in the presence of substances whichenable the hydriding of all said metals of their alloys.

This process is performed with the usual stirring at elevatedtemperature and high pressure, and in accordance with the presentinvention in the presence of a small amount of a surface active agentselected from a group of substances having the same inorganic or metalatom as in the hydride to be produced linked to a hydroxyl group eitherof an alcohol or of a monobasic carboxylic acid both having up to sixcarbon atoms and both containing at least one functional substituent,bonded to another one of the adjacent carbon atoms of the chain, saidsubstituent being selected from the group, consisting of alkoxy-,alkylaminoand amino-substituents and having an atom which is regarded asa donor atom with the available extra electron-pair capable of enteringinto a hole of an acceptor atom. When the number of electron-pairs ofthe donor atom, e.g. oxygen or nitrogen, exceeds the number of itsbonding electrons, then the free electronpair is capable of being bondedby a metal acceptor atom. This effect is probably dependent on thebehavior of the inorganic atom bonded at the end of the hydroxyl groupwhich atom can be either an alkali metal, an alkaline earth metal orboron, aluminum or silicon.

The amount of surface active agent used is not critical, and will bedictated by the type of product desired. Small amounts of less than 1mol percent, for instance of 0.1% are effective in producing anoticeable increase in surface distension of the product. We prefer toadd only 0.2 mol percent of the said surface active agent, calculated onthe molar amount of the metal present, because higher amounts onlypollute the product whereas smaller amounts produce unnecessarily highhomogenization.

It will be appreciated that the term hydride is used in thisspecification to also include a deuteride or tritide as substancesderived from isotopes of ordinary hydrogen. This process, however, alsoyields products in Which only a portion of the hydrogen has beenreplaced by deuterium or a part of the deuterium has been replaced bytritium. Undoubtedly, it is very diflicult be separate any compoundwhich has not been Wholly converted or has been converted only to aminor extent into a deuterium or tritium compound, from the finalproducts in which the deuterium or tritium exchange has taken place to amajor extent.

In accordance with the invention hydrogen is reacted at elevatedtemperature and pressure in the presence of a compound of the generalformula Me'Q wherein Q is an alkoxyl, aroxyl r aralkoxyl selected fromthe group consisting of substituents derived from etheralcohols obtainedby the alkylation of one hydroxyl group in diols and in polyglycols, andsubstituents derived from etheralcohols obtainable by alkylation of twohydroxyl groups in triols and substituents derived from aminoalcohols ofthe general formula R NH C H OH, wherein R is an alkyl, 11

4 is 0, l, or 2, and n is an integer between 1 and 15 and Me is selectedfrom the group consisting of alkali metals, alkaline earth metals, B,Al, and Si, r being the valence of Me.

DETAILED DESCRIPTION Among the substances which may be used as thesurface active agents of the present invention are the metal alcoholatesand metal salts of corresponding monocarboxylic acids derived frometheralcohols having the general formula noc rr orr wherein R ishydrogen, C H C H (OC,,H or

n 2n)m R is aryl with 6 to 8 carbon atoms, or aralkyl with 7 to 8 carbonatoms,

p is 1 to 6, n is 2 to 6, and m is 1 to 3;

aminoalcohols having the general formula R NC H OH wherein R ishydrogen, lower alkyl having 1 to 6 carbon atoms, or

If RN(CnH2n)m n is 2 to 5;

m is 1 to 3; and R" is hydrogen or lower alkyl having I to 6 carbonatoms;

7 aminoetheralcohols having the general formula R is hydrogen or a loweralkyl group having 1 to 6 carbon atoms,

X and Y are different and are selected from the group consisting ofoxygen, -NH- or NR-,

n is 2 to 6, and

m is 1 to 3.

It is evident that besides primary aminoalcohols, secondary bisandtertiary tris-hydroxyalkylamines may be used.

Among the corresponding monocarboxylic acids are those derived fromethercarboxylic acids having the general formula ROC H COOH, aminoacidshaving the general formula R NC H COOH or from amino ether acids havingthe general formula Cyclic etheralcohols, aminoalcohols oraminoetheralcohols where R is cyclohexyl-, phenyl-, toly1-,tetrahydrofurfuryland tetrahydropyranyl-derivatives such as phenylCellosolve may also be used.

The substances used as surface active agents can be referred to as metaletheralcoholates where with exception of the hydroxyl oxygen all otherether oxygen atoms could be replaced by an alkylamino-group whereby thethus obtained N-dialkylamino-etheralcoholates are of such structurewhere at least one of the ether groups is substituted by an alkylamineor dialkylamino-group advantageously so that all thus obtainedamino-groups are tertiary groups.

As the effect of the agents used is determined by both terminal functiongroups i.e. by the hydroxyl group and by the donor atom it is obviousthat the fundamental chain C H or C H can be modified or cyclicized indifferent manner. It is therefore possible to use with the same effect,for instance, alkoxycyclohexanol or N-dialkylamino-benzoic acid.

It is equally obvious that it is possible to introduce into the reactionmedium the substances from which the agents are produced, such as estersof the said alcohols or acids i.e. ether-, aminoor aminoetheralcohols orether-, aminoused instead of the so-called methyl Cellosolve. Thereaction proceeds in a similar manner yielding 58.9 of 95% lithiumhydride, corresponding to 98% of theoretical. The product is again awhite voluminous powder.

or aminoetheracids, as for instance, beta-methoxyethylester of aceticacid CH COO.CH CH OCH ethylester of EXAMPLE 3 methoxyacetic acid CH OCHCOO.C H or N-dimeth- Into the same autoclave were introduced, 62 g. of77.5% yl-beta-aminoethylester of methoxyacetic acid (2 mol) magnesiumand 2 ml. of 'y-phenoxypropanol C H OCH CH CH OH, so-called phenylCellosolve, to- CH3OCI-I 2COO'CH2CH2N( CH3)2 10 gether with steel ballsfor stirring the reaction mixture. As to the explanation of themecharusm of the surface The autoclave was then fill d with hydrogen gasat 3 active agents here in question, it y he assumed that a pressure of100 atm. The reaction starts at 210 C. and small amount of the saidsubstances causes a substantial is fi i h d with 5 hours at c The yieldis 65 g lhefease of the specific shrfaee of the P f hyfirldesof 78.4%magnesium hydride corresponding to 98% of This effect can be explainedby substantlal reduction of theoretic-ah The product is a grayish butvoluminous loss of the surface tension or by transition of same to apowder negative surface tension, the so-called surface distension.EXAMPLE 4 While the surface tension causes an agglomeration of massparticles, as is the case in the course of forming liquid Into the sameautoclave, there Were introduced 164 5%- drops, the surface distensioncauses a fine dispersion state 11101) of Calcium in the form of shavingsand 2 or an increase f the di i f a nomwettahle mass oftetrahydrofurfurylalcohol, and. a stirring rod is used which isanalogous to the creation of emulsions and colfor mixing the reactionmixture as in EXaIhPie The loidal solutions between liquids. A similarphenomenon in exothermic reaction starts at under Consumption lid statemass i fo instance, h creation of Spongeof hydrogen. The reactionmixture is heated in the course ous lead in the course of formingaccumulator electrodes 0f the interaction P to The reaction is finishedor in the course of atomizing metal electrodes of a burn- Within half anhour and the Yield is 163-5 of 93% ing arc column immersed in a liquidwhere colloidal metal eillm hydride in the form of White VehlmihoilsPOWder solutions are created with the co-action of electric energy.Corresponding to 96% of theoretical- The invention will next beillustrated in greater detail EXAMPLE 5 with reference to the followingexamples. D

Into a 2.5-l1ter rotating autoclave there were intro- EXAMPLE 1 duced agiven amount of metal, surface active agent and Into an autoclave of avolume of 2.5 liters, there were siX steel balls of a diEIIIleier 0f 30acting as stirring introduced 50 g. (7.17 mol) of lithium and 2 ml. ofbetameansy for the Pmdueiieh of magnesium hydride methoxyethanol CH OCHCH OH, so-called methyl Celwere a larger number of smaller steel ballsof a diameter 1 1 A ti i d i d f i i th ti of 12 mm. used. Theautoclave, after having been flushed mixture. Hydrogen gas at a pressureof 100 atmospheres With hydrogen, is filled With hydTOgeh at a Pressureof is introduced into the autoclave and the autoclave is sub- 100 Theautoclave Was subsequently heated to the sequently heated. The reactionstarts at 170 C. and at reaction temperature for the time required forthe whole 220 C. an exothermic reaction takes place, consuming 40reaction Process as g as hydrogen gas is Consumedhydrogen gas. Thereaction is completed within half a The reaction temperature varieswithin the range of 200 h Th i ld i 575 f 97% lithi h d id up to 300 C.and for exothermic reactions rises in some responding to 97.7% oftheoretical. The product is in eases uP150 f of a hit voluminous powdenAfter cooling, the residual hydrogen is discharged, the product isemptied using a sieve for retaining the steel EXAMPLE 2 balls. Theproduct is weighed, analyzed and its purity de- Into the same autoclaveas in Example 1 the same initermined. A product of a specific surfacefrom 0.5 to 3.6 tial substances were placed with the difference that 2,sq. m./ g. has been obtained in all cases mentioned in the m1. ofN-dimethylaminoethanol (CH NCH CH OH was following Table I.

TABLE I Weight Weight Time Yield Yield in Number Metal in g. Agent in g.(minutes) in g. percent Purity 5 Li CH3O(CHz)aOLl 2 25 57. 98.1 97.4

6 L1 50 OH -Q-OCHgCHzCHzOH 2 35 58.37 99.2 97.2

7 N9. 100 Q-QCHgCHzONa 2 106.16 99.0 97.3

8 Li 50 B(OCH2CHZOOH3)3 1.8 55 58.63 98.1 95.6

9 Li 50 OH 2 40 58.34 97.3 95.3

N(CH:1)2

CHzOK O TABLE I-Contlnued Weight Weight Time Yield Yield in Number Metalin g. Agent in g. (minutes) in g. percent Purity 45 Sr 87. 6 CHQN 2 3090. 34 97. 2 96. 4

46 Na 100 CH3COOCH2CH2O CH 2 40 106.95 97.5 95.1 47 Na 100 CHaO (31120 O0 CzHs 2 45 105. 10 96. 9 96. 2

EXAMPLE 6 Into a 2.5-liter autoclave with stirring means there wasintroduced a dispersion of a metal with a surface active agent. Theautoclave is closed and connected to a hydrogen pressure source by wayof a pressure reducing valve. After blowing-out and filling withhydrogen at a pressure of atm. the reaction mixture is heated whilestirring at 200 revolutions per minute. After a reaction temperature hasbeen achieved, the autoclave is maintained at a constant pressure of 10atm. for the entire reaction period. The reaction temperature of about200 up to 300 C. is maintained. After the reaction is finished, theautoclave is cooled and emptied. The product was weighed, analyzed andthe purity of the same expressed in relation to the dry state as shownin Table 1 1.

The primary dispersion of lithium, sodium or potassium was prepared byemulgation of the molten metal in the dispersing medium used, usuallyoil, using a homogenizer. The dispersion of other metals can be preparedfrom fine shavings, chips or file dust.

consisting of alkali metals alkaline earth metals, boron, aluminum, andsilicon linked to the hydroxyl group of either an alcohol or amonocarboxylic acid both having up to six carbon atoms and bothcontaining at least one functional sustituent, linked to a carbon atomof the chain other than the carbon atom to which the hydroxyl group islinked, said substituent being selected from the group consisting ofalkoxy-, alkylaminoand amino-substituents, having an atom which isregarded as a donor atom with the available extra electron-pair capableof entering into a hole of an acceptor metal atom.

2. An improvement as set forth in claim 1 wherein said surface activeagent is a metal alcoholate derived from etheralcohols having thegeneral formula ROC H- OH, wherein R is hydrogen, C H C H (OC H or R(OCH R being aryl with 6 to 8 carbon atoms, p being 1 to 6, n being 2 to 6,and in being 1 to 3.

3. An improvement as set forth in claim 1 wherein said surface activeagent is a metal alcoholate derived from aminoalcohols having thegeneral formula R NC H OH TABLE II Disper- Metal 011 Weight Time YieldYield No. slon cont. cont. Agent in g. (minutes) in g. in percent Purity49 446 Na 46 400 CH30CH2CH2OH 1 10 50. 2 98.6 94. 3 50 440 Li 400(CH3)2NCH2CH2OH 1 30 48.1 97.2 93.3

CH 51 450 K 400 NCHzCHzOH 1 10 54. 1 98.0 92. 9

CZHE

52 460 Ca 60 400 (CH3)2N(CzH Oz)H 1 30 66.3 97. 6 92.7 53 r. 546 Na 46500 H2N(CH2)20(CH2)2OH 1 15 50.8 96. 9 91. 5 54 646 Na 46 600(CH3)2NCH2CH2COON3 1. 5 20 50.0 97. 5 93.6

(F113 55 496 Na 46 450 (CH3)zNCzH4NCzH4OH 1 10 58. 5 97.7 96.8

(3H3 56 435 L1 35 400 (CH3)2NC;H4NC4H3OH 1= 25 41.8 97.1 93.0

57 535 L1 35 500 C2H5OC3HsNC2H4OH 20 41.6 97. 8 94. 2

Toluene.

EXAMPLE 7 wherein R is hydrogen, lower alkyl having 1 to 6 carbon Intothe same pressure vessel as in Example 1 were charged 100 g. Na (4.34moles), 2 g.

(CH3 NCH CH ONa and a stirrer. Deuterium of 99.65% D-purity wasintroduced into the pressure vessel to establish a pressure of 75atmospheres. The reaction started at 270 C.; the temperature was kept inthe range between 270 and 310 C. The reaction was finished after 105minutes; 109.7 g. of sodium deuteride was obtained, containing 96.3% NaDof a 99.03% D-purity, i.e., 97% of theoretical. The specific surface ofthe product, which was obtained in form of a fine white powder, amountedto 2.8 m. g.

What is claimed is:

1. In a process for preparing a hydride of an alkali metal, and alkalineearth metal or magnesium by direct interaction of the metal or metalalloy with hydrogen gas with stirring at elevated temperature andpressure, an improvement comprising effecting the interaction in theabsence of any dispersion medium and in the presence of a relativelysmall amount of a surface active agent having an inorganic or metal atomselected from the group atoms, or

n is 2 to 6; m is l to 3; and R" is hydrogen or lower alkyl having 1 to6 carbon atoms.

4. An improvement as set forth in claim 1 wherein said surface activeagent is a metal alcoholate derived from aminoetheralcohols having thegeneral formula acid corresponding to the said animoalcoho'ls andderived from amino-acids having the general formula 7. An improvement asset forth in claim 4 wherein said surface active agent is a metal saltof a mooncarboyxlic acid corresponding to the said aminoetheralcoholsand derived from amino-etheracids having the general formula R(XC,,H--YC,, H COOH.

8. In a process as set forth in claim 1 the further improvementcomprising introducing substances into the reaction mixture, from whichthe surface active agent is produced in situ under the reactionconditions.

9. An improvement as set forth in claim 8 wherein said substances whichare introduced into the reaction mixture, from which the surface activeagents are produced under the reaction conditions, are esters of saidalcohols or monocarboxylic acids.

10. In a process for preparing ionic hydrides and/or deuterides and/ortritides of alkali metals and alkaline earth metals inclusive ofmagnesium by the interaction of hydrogen with the metals at elevatedtemperatures and pressure while stirring, an improvement comprisingeffecting said process in the absence of any dispersing medium and inthe presence of compounds of the general formula Me Q wherein Q is analkoxyl, aroxyl or aralkoxyl selected from the group consisting ofsubstituents derived from etheralcohols obtainable by the alkylation ofone hydroxyl group in diols and in polyglycols, and substituents derivedfrom ether-alcohols obtainable by alkylation of two hydroxyl groups intriols and substituents derived R NH O H O I-I, wherein R is an alkyl, his 0, 1, or 2, and n is an integer between 1 and 15, and Me is se- 12lected from the group consisting of alkali metals, alkaline earthmetals, B Al and Si, and r is the valence of Me.

11. An improvement as defined in claim 10 wherein Q is CH OCH CH O andwherein the hydrogen, Me, and CH OCH CH OH are charged into and reactedin a reaction pressure vessel.

12. An improvement as defined in claim 11 wherein Me is lithium and thereaction is carried out at to 360 C.

13. An improvement as defined in claim 11 wherein Me is sodium, and thereaction is carried out at 220-300 C., the CH OCH CH OH being chargedinto the said vessel in an amount between 0.003 and 0.1 molar percent ofthe molar amount of sodium, the reaction thus being carried out in thepresence of NaOCH CH OCH which is formed.

14. An improvement as set forth in claim 1 wherein the relatively smallamount of said surface active agent is less than 1 mol percent based onthe molar amount of the metal.

References Cited UNITED STATES PATENTS 2,372,670 4/1945 Hansley 232042,392,545 1/ 1946 Pechet 23204 2,768,064 10/ 1956 Baldridge 23-2042,946,662 7/ 1960 Mosely 23204 3,222,288 12/1965 Hansley 23-2042,642,344 6/1953 Livingston 252.309X

FOREIGN PATENTS 1,421,346 1965 France 252-309F OSCAR R. VERTIZ, PrimaryExaminer G. O. PETERS, Assistant Examiner

